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BUG: KCSAN: data-race in __process_echoes / n_tty_write

write to 0xffffc90001cc3278 of 8 bytes by task 31770 on cpu 1:
 __process_echoes+0x603/0x650 drivers/tty/n_tty.c:751
 flush_echoes drivers/tty/n_tty.c:812 [inline]
 __receive_buf drivers/tty/n_tty.c:1564 [inline]
 n_tty_receive_buf_common+0x4a0b/0x4c40 drivers/tty/n_tty.c:1658
 n_tty_receive_buf+0x2b/0x40 drivers/tty/n_tty.c:1687
 tiocsti+0x14b/0x1a0 drivers/tty/tty_io.c:2293
 tty_ioctl+0x279/0x970 drivers/tty/tty_io.c:2692
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:856
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

read to 0xffffc90001cc3278 of 8 bytes by task 31769 on cpu 0:
 process_echoes drivers/tty/n_tty.c:789 [inline]
 n_tty_write+0x14e/0xb40 drivers/tty/n_tty.c:2283
 do_tty_write drivers/tty/tty_io.c:1024 [inline]
 file_tty_write+0x3f9/0x650 drivers/tty/tty_io.c:1095
 tty_write+0x24/0x30 drivers/tty/tty_io.c:1116
 call_write_iter include/linux/fs.h:2189 [inline]
 new_sync_write fs/read_write.c:493 [inline]
 vfs_write+0x471/0x770 fs/read_write.c:580
 ksys_write+0xe8/0x1a0 fs/read_write.c:633
 __do_sys_write fs/read_write.c:645 [inline]
 __se_sys_write fs/read_write.c:642 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:642
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x2b/0x70 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

value changed: 0x0000000000000000 -> 0x0000000000000003

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 31769 Comm: syz-executor.0 Not tainted 5.19.0-syzkaller-12567-g1612c382ffbd-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
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